This invention relates to a novel resinous composition containing an acrylic polymer having a plurality of alicyclic epoxide functions. The composition may be cured or crosslinked through the cationic polymerization of the epoxide function and is useful as a resinous component of coating compositions, sealants, potting or casting compositions and the like.
Cationic polymerization of epoxy resins using a cationic polymerization initiator is well-known. Usable initiators include Lewis acids, Friedel-Crafts catalyst, boron trifluoride-ether complex, photodegradable onium salts (S, Se, Te), diallyl iodonium salts and the like. Initiators of this type are generally not selective with respect to the reaction temperature. Therefore, an epoxy resin containing these initiators begins to cure even at room temperature.
Japanese Patent Kokai (Laid Open) application Nos. 37003/83 and 37004/83 disclose another type of cationic polymerization initiator. They are aliphatic or aromatic sulfonium salts capable of generating carbonium cations upon heating to an elevated temperature. Initiators of this type are known as "heat-latent cationic polymerization initiator". U.S. patent application Ser. Nos. 07/356,903 and 07/532,716, both assigned to the assignee of this application, also disclose a heat-latent cationic polymerization initiator. Epoxy resins containing the heat-latent initiators are therefore normally nonreactive but capable of curing at a temperature above the cleaving temperature of the initiator. This provides a heat-curable, one-component epoxy resin composition having a greater storage stability and a longer pot life.
Epoxy resins or polymers used heretofore for this purpose are limited to glycidyl ether or ester epoxy resins, typically bisphenol A epoxy resins, and homo- and copolymers of glycidyl acrylate or methacrylate (hereinafter collectively referred to as "(meth)acrylate").
We have now found that acrylic polymers having a plurality of alicyclic epoxide functions are more sensitive to the cationic polymerization than glycidyl epoxy resins in the presence of a heat-latent cationic polymerization initiator. The present invention has its basis on this finding.